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An Observer Study Evaluating Dual-Plane Circular-Orbit Cone-Beam Brain SPECT

Department of Biomedical Engineering, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina

Dual-plane circular-orbit cone-beam (DPCB) SPECT uses a pair of dissimilar cone-beam collimators to expand the axial field of view for brain SPECT. We applied observer study methodology to evaluate the improvement in detection of small defects in brain perfusion provided by DPCB SPECT, compared with conventional parallel-beam imaging. We also evaluated the effect of changing the radius of rotation on DPCB imaging. Methods: Images were realistically simulated using a brain phantom. High-count Monte Carlo simulations were performed for 4 imaging configurations: low-energy high-resolution parallel-beam imaging at a radius of rotation of 18 cm and DPCB imaging (52-cm focal length) at radii of rotation of 20, 24, and 28 cm. These distances corresponded to those required for our camera to clear the shoulders of a patient in the 5th, 50th, and 95th percentiles of shoulder width. Perfusion defects of 1.8-cm diameter were simulated at 4 locations in the brain. Poisson noise was simulated, and images were reconstructed to create a set of 200 images for each of the 4 configurations. All reconstructions used ordered-subset expectation maximization with attenuation modeling. Eight observers viewed images on which the possible location of the defect was marked. The observers were trained using 384 images, were tested using 416 images, and rated on a continuous scale their confidence about the presence of a defect. Results: Using a paired t test for the estimated areas under the receiver operating characteristic (ROC) curve for each observer, we found that all 3 DPCB configurations resulted in higher areas under the ROC curve than did the parallel-beam configuration. Further, area under the ROC curve for the DPCB configurations improved with decreasing radius of rotation. All comparisons were significant at P < 0.05, except for DPCB 20 cm to DPCB 24 cm (P = 0.089). Conclusion: Use of a dual-plane cone beam is feasible for brain SPECT and better detects small perfusion defects than does a parallel beam, despite the possibility that the radius of rotation will need to be increased significantly to clear the patient’s shoulders. A dual-plane cone beam should be used with the shortest radius of rotation possible to maximize the detectability of small perfusion defects.

Key Words: brain SPECT • cone-beam SPECT

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